I am a dedicated urban forager/harvester, but beach roses are so common and abundant in this area that there's absolutely no reason to browse them from in a location not just chemically but also physically dangerous. That stretch of Comm Ave is one of the most dangerous to pedestrians in the entire city.

If you are jonesing for beach rose hips, there's a huge and healthy 'hedge' of it growing along the platform of the Roslindale Village commuter rail station.

...once they've gone into the soil and been broken down into constituent compounds. Otoh, lead, arsenic, and impacts with 3000 lbs objects traveling at high speed are not just 'icky sounding', but actually dangerous.

Vehicle exhaust no longer contains lead, and the rest will either irritate plants (but not be poisonous) or feed the plants. The arsenic in road salt would likely be negligible if this were from a raised median container.

Also a matter of how much you eat - and this really won't be a huge part of a person's diet anymore.